Conventionally, there are known those tubes of a laminated structure in which the outer layer is laminated onto the substrate layer. These laminated tubes usually have a structure in which the outer layer is laminated uniformly in the peripheral direction of the tube cross-section.
The molded products of a laminated structure, in which an outer layer is laminated onto the substrate layer, are obtained by, for example, co-extruding two different types of synthetic resins or cladding the substrate layer with the second layer. In this cladding method, the substrate layer has already been made into a tube, and is clad with the second layer by an ordinary extrusion-molding process.
On the other hand, the co-extrusion molding method utilizes a molding die that has two or more separate flow paths for the molten resins and lets these flow paths merge within the die. The molding die has such a cross-section that gives the shape of a resinous tube. Two types of resins are molten and run through the respective flow paths. The two layers are welded firmly to each other, and the laminated tube is extruded from the die exit in the cross-sectional shape of the die, and is left to cool.
The laminated tubes made by conventional co-extrusion molding process has difficulty in preventing cuts in the outer layer to be laminated onto the substrate layer and also in cladding the outer layer in the uniform thickness because each synthetic resin has a different softening point and flow resistance. A technology for laminating the outer layer onto the substrate layer at a uniform thickness has been developed to solve this problem.
In the cladding method, too, it is also difficult to clad the substrate layer with the outer layer at a uniform thickness because there is a pressure difference generated in the resin inside the head of the extrusion-molding die. In order for this problem to be solved, a technology has been developed to extrude the outer layer in a pipe shape from the molding die having a diameter larger than the outer diameter of the tubular substrate layer and to make the outer layer stick onto the substrate layer by sucking the outer layer from the nipple side of the die exit under reduced pressure.
However, if the outer layer laminated onto the substrate layer has a uniform thickness, the tube looks even and monotonous and lacks spice, thus giving no decorative effect. Furthermore, the tube cannot be identified simply by touch.
Meanwhile, even in the case where the outer layer laminated onto the substrate layer has some irregularity in molding the laminated tube, it is necessary to produce the irregularity while maintaining certain uniformity if a high-class image is to be achieved in addition to aesthetic appearances.
Consequently, the technical problem of this invention is to laminate the outer layer onto the substrate layer that makes up the main body of the tube, wherein the outer layer is a projecting portion or portions while maintaining certain uniformity. The object of this invention is to provide the tube and the molded tube products comprising the tube, which show the decorative effect derived from the projecting portion(s) and which enable the user to identify the tube by touch, too.